Paleogene Period

Paleogene Period, major division of the Cenozoic Era, spanning the interval from about 65 to 23 million years ago. Scientists made the Paleogene an official geologic period when they revised the geologic time scale in 2004. The Paleogene Period includes the Paleocene, Eocene, and Oligocene epochs, and corresponds to the early part of the Tertiary Period, a formerly used division of the geologic time scale that also included the Miocene and Pliocene epochs (epochs now included in the Neogene Period). The Paleogene Period precedes the Neogene Period (23 million years ago to present day), when more modern types of animals became dominant.

The name Paleogene means 'ancient born' and refers to the more primitive character of the animals that lived during the period. The Paleogene began after a mass extinction at the end of the Cretaceous Period that killed the dinosaurs, and marks the beginning and early development of the Age of Mammals. The top carnivores of the period came from two primitive extinct groups called creodonts and mesonychids, while the large hoofed plant-eaters included the extinct dinocerata, titanotheres, and arsinoitheres. The earliest whales, bats, rhinoceroses, and primates also appeared. One of the warmest periods in Earth's history occurred during the early Eocene Epoch, followed by a major cooling during the Oligocene Epoch. A mass extinction event affecting mainly marine life and land mammals marked the end of the Eocene.